Covert search and detection of illicit nuclear as well as radioactive material
To prevent the misuse of nuclear or radioactive material for malicious acts we investigated highly sensitive passive detection systems for gamma and neutron radiation. The aim is to detect such material as early as possible with high reliability excluding false alarms caused by natural radioactivity (like in potash fertilizer) or by patients which have undergone a nuclear medical therapy respectively examination. Fixed monitors can be employed for the detection of such materials during transport. They may be covertly installed in advertising pillars or other objects commonly found in public. In a more static situation a general overview is gained by scanning of buildings or objects with a gamma camera. Here the measured spatial gamma intensity is converted into colors and then superimposed on the optical picture of the situation in order to get a visual overview. Besides gamma detectors we investigated neutron detectors also. Nuclear material can be detected by neutron emissions from spontaneous fission as well as by the neutrons produced by (alpha,n) reactions in surrounding material. Therefore we operate a sensitive neutron detection system, fitted into a hand pulled suitcase. With a special analysis procedure it is possible to categorize the substance in fissionable and non-fissionable material. In addition, the system can discover the existence of shielding material located around the source material. The presence of shielding material often gives important information for the evaluation of the possible risk. Furthermore a specific search can be executed when a concrete suspicion arises. Therefore we investigated the characteristics of small, hand-held devices for in field operation.